Pressure control system



Aug. 14, 1962 J. M. BOURGUET ET AL 3,049,013

PRESSURE CONTROL SYSTEM Filed Oct. 20, 1958 4 Sheets-Sheet l INVENTORS.

Jean M.B0urgue1 Roberr D.Drew

" AQQMMZ.

ATTOR Y.

Aug. 14, 1962 Filed 061;. 20, 1958 J. M. BOURGUET ET AL PRESSURE CONTROLSYSTEM 4 Sheets-Sheet 2 52 53 55 57 6l so 7 055K WM r r' FIG.2

Uni-directional g 65 67 Valve J Pressure Differential Process 2Trunsmiher Chamber Uni-directional 75 Valve 70 Pressure RecordingApporufus INVENTORS.

FIG.3

Jean M.Bourguet Robert D.Drew

ATTORN EY.

1952 J. M. BOURGUET ETAL 3,049,013

PRESSURE CONTROL SYSTEM Filed Oct. 20, 1958 4 Sheets-Sheet I5 45 47Pressure Differential Transmitter Pressure Recording Apparatus mmm \JKJ

FIG.4

Pressure Differential y 47 Transmitter 4o 48 Uni-directional L J 44 42Valve 49 Pressure Recording Apparaius Fl (3 5 //v VEA/ TORS. JeanM.B0urguei Robert D.Dr

by QMMQM AT RNEY.

Aug. 14, 1962 J. M. BOURGUET ET AL 3,049,013

PRESSURE CONTROL SYSTEM Filed Oct. 20, 1958 4 Sheets-Sheet 4Uni-directional 67 Valve GAS PROCESS 66 LIQUID 2 74 PressureDifferential Transmitter 65 I I Uni-directional GAS Valve Recorderand/or Control Apparatus Uni-directional Valve Transmitter or PressureBooster/ Uni-directional Valve FIG.7

Recorder and/or Control Apparatus IN VENTORS. Jean M.'Bourguet RobertD.Drew

ATTO NEY.

nite rates "lie 3,049,913 PRESSURE EONTROL SYSTEM Jean M. Bourguet,Woodbury, and Robert D. Drew,

Wenonah, N.J., assignors to Socony Mobil Oil (30mpany, Inc, acorporation of New York Filed Oct. 20, 1958, Ser. No. 768,310 7 Claims.(Cl. 73388) This invention relates to instrumentation for directmeasurement of the amplitude of the fluctuation of pressure in a processzone as a continuous function and to make control of this amplitudepossible. It is particularly applicable to the control of a pneumaticlift used to elevate granular catalyst in a stream of rapidly risinglift gas for recycle in the moving bed hydrocarbon conversion processes.

Various processes, such as cracking, reforming, coking, desulfurization,etc. use a granular contact material or catalyst with the hydrocarbonsbeing brought into contact with the catalyst under pressure andtemperature conditions found to permit eflioient conversion of thehydrocarbons to more desirable products. The TCC or Thermofor CatalyticCracking process is the most widely used moving bed process and recentTCC units have utilized a pneumatic lift for elevation of the granularcontact material. This invention will, therefore, be described withrespect to its application in the TCC process. It Will, of course, beappreciated that the invention finds application in a variety ofprocesses and is not limited solely to the TCC process.

In the TCC process the catalyst is gravitated as a continuous columnfrom the lift hopper, through an elongated vertical feed leg into anadvanced pressure reactor, from the bottom of the reactor downwardlythrough a kiln and from the bottom of the lciln to a lift pot. Theparticles are propelled in a rapidly moving stream of lift gas, usuallyair, from the lift pot through a lift pipe to the elevated liftseparator. The particles travel in dispersed form, accelerate rapidly inthe lower portion of the lift pipe to a maximum velocity and thengradually drop in velocity to a desired low discharge velocity. The pipeis usually tapered to accomplish the proper velocity control.

The critical features of catalyst velocity control in the lift have beendeveloped and are described now in the patent literature. It issufficient for this application to state that there is a minimumpressure drop across the lift for any given set of conditions whichproduces minimum attrition and that this point can be found by reducingthe total air to the lift until the pressure drop across the liftreaches a minimum and commences to increase with further gas reduction.While these facts are well known now, it is difficult to continuouslymaintain a pneumatic lift in operation at the point of minimum attritionbecause of slight changes in gas flow, temperature, pressure, etc. whichoccur in the process. The lift tends to drift from the point of minimumattrition and any movement from this point results in undesirableincrease in attrition. Unfortunately, this drift is diflicult torecognize and unnecessary catalyst dam-age occurs long before the shiftcan be recognized.

This invention is based on the observation that the fluctuation of amain variable, such as the pressure in a pneumatic lift pipe, is often abetter indication of the stability of the operating conditions than themain variable itself. When upsets are beginning to take place, thefluctuation of the main variable often increases before the absolutevalue of the variable starts to change appreciably. Also, the ratio offluctuation of the main variable to the value of the main variable isoften so small that it does not even appear on the recorder orindicators used to measure the main variable. This is decidedlyunfortunate since the detection of the fluctuation of the main variable,such as, for instance, the fluctuation of pressure in a pneumatic lift,would give a warning in case of an approaching upset in lift conditionsand hence correction could be made before any real damage took place.Detection through the main variable, such as the pressure in the liftpipe, is possible but often too slow to give a warning and the upset inoperating conditions is so advanced when detected by observation of themain variable that damage has been done to the process and a loss hasalready been suffered. As an example, in a pneumatic lift operationelevating granular catalyst in a TCC system, an increase of the pressurein the lift pipe of 25 percent means that the operation has gone into anundesirable surging condition. The corresponding increase of thefluctuation in pressure is 5 0 percent and hence it is seen that thepressure fluctuation is a far more sensitive indicator than the pressureitself.

The object of this invention is to provide a method and means ofsuppressing a main pressure variable in a process while keeping only thefluctuation of the pressure for record on a zero-centered instrument.

A further object of this invention is to provide a method and means ofsuppressing a pressure variable in a process while keeping only thefluctuation of the pressure for record on a zero-shifted instrument.

A further object of this invention is to provide a method and means ofmeasuring the average amplitude of fluctuation of pressure in a processto permit this average amplitude to be used for control purposes.

These and other objects will become obvious from the following detaileddescription of the invention to be read in conjunction with the attachedfigures.

FIGURE 1 is a diagrammatic representation of a TCC system with theapparatus of the invention incorporated for lift control purposes.

FIGURE 2 is a vertical sectional view showing valve control meansdeveloped as a part of this invention.

FIGURE 3 is a diagrammatic showing of apparatus arranged in accordancewith the invention to indicate average pressure amplitude.

FIGURE 4 is a diagrammatic showing of apparatus arranged in accordancewith the invention to indicate pressure fluctuation on a zero-centeredinstrument.

FIGURE 5 is a diagrammatic showing of apparatus arranged in accordancewith the invention to indicate pressure fluctuation on a zero-shiftedscale.

FIGURE 6 is a diagrammatic showing of apparatus arranged in accordancewith the invention to indicate pressure fluctuation of a processingliquid which. has a fluctuating pressure during operation of theprocess.

FIGURE 7 is a diagrammatic showing of apparatus arranged in accordancewith the invention to indicate pressure fluctuation in readablemagnitude when the pressure fluctuation in the process is too feeble tobe used directly.

In one important aspect, the invention involves communicating a firstand second pressure indicating zone with a process zone to permit fluidto transfer from each zone to the other and sufliciently restricting thetransfer of fluid between the first and second indicating zone todevelop between the two zones a pressure differential which is directlyrelated to the pressure fluctuation in the process zone so that thispressure differential can be read directly and used to effect control ofthe operation of the process. The invention will now be described indetail first by a discussion of the T CC process where the invention isused to control the operation of the pneumatic lift at maximumefliciency operation with minimum attrition.

Referring now to FIGURE 1, a diagrammatic showing of a TCC system, areactor 10 is shown in superimposed position with a kiln 11 of annularcross-section through which is located a vertically extending pneumaticlift pipe 12. At the base of the lift pipe is located a lift pot 13 andassociated gas apparatus for elevating the catalyst in dilute phase formthrough the lift pipe 12 to a separator 14. The gas and catalystseparate in the separator 14, the gas being discharged to the atmospherethrough the pipe 15, the catalyst settling to the base of the separator14 to form a compact gravity flowing mass. Catalyst is withdrawn fromthe bottom of separator 14 through an elongated gravity feed leg 16 intothe reactor 14} which is maintained under advanced pressure andtemperature. A seal gas such as steam or flue gas is introduced into thelower section of the gravity feed leg through a conduit 17 controlled bythe valve 18 by means of a suitable feed pot 19. This gas is introducedat slightly higher than reactor pressure so that some gas will flowdownwardly with the catalyst into the reactor to prevent the escape ofreactants from the reactor. The remainder of the seal gas flows upwardlythrough the seal leg countercurrently with the catalyst and escapes tothe atmosphere through the vent pipe 20. Suitably prepared hydrocarbonreactants are introduced into the reactor through the conduit 21 andtravel concurrently with the catalyst and through the void spaces in thebed to the lower section of the vessel. The conditions are maintained sothat a substantial amount of the reactants are cracked in the presenceof the catalyst to provide an increased amount of high octane motorfuel. The reaction products are withdrawn from the catalyst through theconduit 22 and pass through suitable processing apparatus not shown.During the cracking reaction a carbonaceous deposit is formed on thecatalyst and the spent catalyst is Withdrawn continuously from thebottom of the reaction vessel 10 through the multiplicity of conduits 23and transferred to the top of the kiln 11. Air is introduced into thegravitating bed of catalyst in the kiln 11 through the conduit 24. Aportion of the air travels upwardly through the bed to burn a portion ofthe contaminant on the catalyst, the flue gas being discharged to theatmosphere through the conduit 25 located near the top of the Vessel.The remainder of the air travels downwardly through the catalyst bed tocomplete the combustion of the contaminant, the flue gas beingdischarged to the atmosphere through the conduit 26. The regenerated andreheated catalyst is withdrawn from the bottom of the kiln through theconduits 29 and introduced into the lift pot 13. It is seen that thecatalyst travels as a continuous compact gravitating stream from thehopper 14 downwardly through the various vessels to the lift pot 13. Thespeed of gravitation of the catalyst is controlled by the rate ofremoval of catalyst from the lift pot 13 through the lift pipe.

A blower 30 is used to provide air under a modest pressure of, forexample, 5 to 10 p.s.i.g. or less to the lift. The air travels to theconduit 31, the flow being measured by the meter 32. This air stream isthen split into a secondary'stream 33, which is introduced into thecatalyst bed around the lower end of the lift pipe and is used tocontrol the flow of catalyst into the lift pipe. The remainder of thelift gas is passed through the conduit 34 which projects upwardly intothe bottom of the lift pipe and introduces this air stream into the liftpipe without passing through any substantial thickness of catalyst bedin the lift pot 13. By this expedient the total flow of air can becontrolled independent of the flow of catalyst. The flow measuringinstrument 32 is connected to controller 35 which operates automaticvalve 36 in line 34 to maintain the total flow rate of air to the liftsubstantially constant. A controller 37 is connected to the top of thelift pot 13 by the conduit 38 and the controller operates an automaticvalve 39 so as to maintain the pressure in the upper portion of the liftpot substantially constant, thereby maintaining substantially constantcatalyst flow.

It has been discovered that for minimum attrition in the pneumatic liftthe velocity conditions of the catalyst must be carefully controlled. Arapid acceleration is desirable in the lower portion of the lift up to amaximum critical velocity, at which point the catalyst must then begradually reduced in upward velocity to a critical discharge velocity.Slight changes in velocity pattern of the catalyst in the lift willcause substantial change in efliciency of operation of the lift anddamage to the catalyst or attrition rate. These facts have beendiscussed fully and completely disclosed in Patent Number 2,819,121issued January 7, 1958. The patent teaches that for control of a lift ofthis type so as to provide minimum attrition in the lift, the gas flowthrough the lift must be controlled to maintain a pressure fluctuationin the upper portion of the lift at a fixed ratio of the pressurefluctuation at the bottom of the lift. This invention provides a methodand means for automatically reading or controlling the lift as a resultof such reading of the pressure fluctuation in the upper portion of thepneumatic lift. While the invention was made to solve this specificproblem, it of course has broader application and can be used in manyother circumstances where a measure of pressure fluctuation is avaluable indicator.

Referring now to FIGURE 4, 4 19 represents a vessel in which a pressurefluctuation is taking place. Vessel 4% may be a portion of the lift pipe12 of FIGURE 1. Attached to the vessel 4th by means of a conduit 41 is achamber 42. The connection at between vessel and 42 is arranged so thatthe pressure in chamber 42 follows quite faithfully the pressure in thevessel .10. A second chamber 43 is attached to the chamber i2 by meansof a conduit 44. In the conduit 44 is a flow restricting device 45 sothat there is restricted communication between the chambers 4-2 and 4-3.For any given pressure fluctuation this flow restriction can be adjustedso that chamber 43 will reach a pressure intermediate between themaximum pressure obtained in chamber 42 and the minimum pressureobtained in chamber 4 2, and furthermore this flow restriction can be soadjusted that the pressure in chamber 43 remain substantially constant.Chamber 42 is connected by means of conduit 46 to a pressuredifferential transmitter 47, and chamber 4-3 is connected by conduit 48to the same pressure di'lferential transmitter. Thereby the pressuredifference between chambers 42 and 43 can be read directly andtransmitted by connection 49 to a pressure recording apparatus 5 3?. Itis seen that by this expedient a full-scale direct reading zero-centeredindication of the pressure differential occurring in vessel 46 isprovided. Hence, even though the pressure fluctuation in the vessel 40may be only a very small portion of the absolute pressure in the vessel,it can be measured as a full-scale reading by the apparatus of thisinvention.

FIGURE 5 shows a modification of the apparatus in which the fluctuationis recorded as a full-scale reading on a pressure recording apparatusbut with the zero of the instrument displaced from its center position.The apparatus arrangement is very similar to the apparatus of FIGURE 4and hence identical numbers have been used for identical pieces ofapparatus. In the apparatus combination of FIGURE 5, however, in placeof the flow restricting device 45, a unidirectional valve 51 is used.Suitable unidirectional valves adapted to operate on very slightpressure differential were not found in the market and hence theapparatus combination of FIGURE 2 was designed for this purpose.Referring now to FIGURE 2, the conduit 52 connects to the chamber 42 andhas in it a jet 53 designed to control the flow rate of the air from thechamber 42 to the chamber 43. A valve plate 54 hinged at one end 55 isadapted to close over the end of the conduit 52. A spring 56 is locatedbetween the plate 54 and a fixed bracket 57 so as to provide bias towardthe closed position. A connecting rod 58 is attached to the valve 54 andextends through the body 59 of the valve. A cap 60 is threaded on theend of the connecting rod 58 and designed to put variable tension onspring 61. By this arrangement a fine adjustment of the closing pressureon the valve plate 54 can be maintained. By appropriate adjustment ofthe valve springs, gas will flow from chamber 42 to :3 when the pressurein the chamber 42 is sufficient to open the valve, but when the pressurein the chamber 42 drops, the valve will close preventing the flow of gasfrom the chamber 43 to the chamber 42. By appropriate adjustment thepressure in the chamber 43 can be adjusted to substantially the maximumpressure occurring in the chamber 48. In processes of this type unusualpressure fluctuations occur from time to time and in order to preventchamber 43 from indicating only unusually high pressure fluctuations, ableed orifice 62 is located in the pipe 52 and an adjustable needlevalve 63 is provided so that only a very small bleed stream of gas ispermitted to transfer back from the chamber 43 to the chamber 42. Thiswill permit the chamber 43 to com pensate for unusual pressurefluctuations and will permit the chamber 63 to indicate generally themaximum pressure occurring in the chamber 4! As seen, therefore, on thepressure recording apparatus 64, the zero of the indicator has beenshifted by this apparatus combination to one side of the meter so thatthe pressure fluctuation can be read full scale on a zero-shiftedinstrument.

For control purposes it is highly desirable to have the fluctuation ofpressure indicated as a substantially constant value between maximum andminimum limits. The apparatus combination of FIGURE 3 is adapted toprovide this result. The process chamber 65 is connected to a conduit66. A conduit 67 is connected to a detecting chamber 63 and has in it aunidirectional valve 69 so that fluid is permitted to flow only from theprocess chamber into the detecting chamber 68. Another conduit 79 isconnected to the conduit 66 and also to a detecting chamber 72.. In theconduit 76? is located a unidirectional valve 72 arranged to permitfluid to flow only from the detecting chamber 71 to the process chamber65. By this arrangement the maximum pressure occurring in the processchamber will be maintained in the detecting chamber 63 whereas theminimum pressure occurring in the process chamber 65 will be maintainedin the detecting chamber 711. It will be understood, of course, that theconduits 67 and 70 could be connected directly to the process chamber aslong as their connection was sufficiently close to each other. A bleedline 73 with valve 74 therein is provided to maintain a very slight flowof gas between chambers 68 and 71. It is apparent that without such ableed, chamber 68 would maintain a pressure equal to the highestpressure which had occurred in the process at some earlier time, andlikewise chamber 71 would maintain a pressure equal to the lowestpressure which had occurred in the process at an earlier time. Thedevice would then not be indicating the current maximum and minimumpressures, and would, in effect, be inoperative. The slight flow offluid between chambers 68 and 71, and through bleed line 73 and valve74-, will relieve these high and low pressures to a level where thepresent pressure levels existing in the process will determine thepressures in chambers 68 and 71 by passing through unidirectional flowcontrol means 69 and 72. This flow can be made so small that it willnormally have no substantial effect upon the pressure differentialmaintained between the first detecting chamber and the second detectingchamber. The first detecting chamber is connected to a pressuredifferential transmitter 7 5 by means of connection 76 and the seconddetecting chamber is connected to the pressure differential transmitter75 by means of connection 77. This substantially constant pressuredifferential, being a measure of the amplitude of pressure fluctuationin the process chamber 65, can thereby be transmitted directly to apressure recording apparatus 78 providing a substantially uniformreading. Alternatively, this pressure differential can be used tooperate known apparatus for adjusting conditions in the process chamberto maintain the pressure differential substantially constant. Thisapparatus combination is particularly useful in the con- 5 trol ofpneumatic lifts such as is indicated in Patent Number 2,819,124 whichissued January 7, 1958.

Referring to FIGURE 6, there is shown an apparatus combination similarto that disclosed on FIGURE 3 but adapted for use particularly with aprocess liquid. Similar elements have been given similar numbers forsimpliflcation of description.

It is seen on FIGURE 6 that liquid is transferred from the processchamber 65 to the first detecting chamber 68 when the pressure reachesthe maximum in the chamber 65, and liquid is transferred from the seconddetecting chamber 71 when the pressure in the process chamber 65 reachesits minimum value. A diaphragm 79 is located across the first detectingchamber 68 to separate the chamber into a liquid compartment and a gascompartment. Similarly, a diaphragm Si is located across the seconddetecting chamber to also separate this chamber into a liquidcompartment and a gas compartment. By this arrangement the pressure istransmitted from an incompressible fluid to a compressible fluid and thepressure is then transmitted through the compressible fluid to thedifferential transmitter 75. This pressure ditferential can then be usedto operate a recorder or a control apparatus in a manner similar to thatdescribed with respect to FIGURE 3.

FIGURE 7 shows a somewhat similar arrangement to that disclosed withrespect to FIGURES 3 and 6 but provides additionally means forincreasing the pressure differential indication so as to facilitate theuse of pressure differential for control purposes. The same numbers havebeen used to identify the same parts as used in FIGURES 3 and 6. Whilethis embodiment is obviously very similar to that disclosed with respectto FIGURE 3, there is located in the conduit 66 a transmitter orpressure booster 81. This pressure booster has the ability to increasethe pressure indication it receives from the process chamber 65 a fixednumber of times. By this expedient the pressure maintained in the firstand second detecting chambers is substantially increased and thedifferential maintained between these chambers is also increased. Thisis necessary in many instances because pressure recording or controlapparatus operates more efficiently under substantial pressure. Thetransmitter or pressure booster 81 will not be described here in detailas it is commercially available in a variety of forms. Pneumatictransmitters for this application would normally have an output signalranging from a minimum of 3 p.s.i.g. when the input signal was at itsown minimum, to a maximum output of 15 p.s.i.g when the input signal wasat its own maximum. The input range of the transmitter must besufliciently large so that the process conditions are at all timeswithin that range. A typical pneumatic transmitter for this use inconnection with the monitoring of TCC lift pipe pressure fluctuation hasan output range of 3 to 15 p.s.i.g. when the input signal varied from Oto l p.s.ig. for full range An example of a commercially availabletransmitter of this type would be a Taylor Model No. 206RF2.

Description of Reduction to Practice The method and equipment describedherein were used to control a pneumatic lift elevating granular catalystby means of an air stream. This lift had the following characteristics:

The apparatus was operated at optimum conditions for minimum attrition,and also at conditions of too high and too low lift air rates, both ofwhich give excessive catalyst attrition. The following characteristicsof operation for the apparatus of this invention were obtained:

Lift Air Rate, Percent of 110 High 100 Opti- 95 Surg- Optimum. Velocity.mum. ing.

Pressure, 82 Ft. Elevation in {6.4 HzO 10.5 HZO 13.5 H20.

Lift Pipe, H20 and p.s.i.g. 0.23 0.38 0.49.

Percent Change from Opti- 40 30.

mum.

Pressure Fluctuatioiii, 8% Ft. 2.2 H10. 4.4 1320.-.. 6.7 H 0.

Elevation in Li t ipe, 4 H20 and Sig. 0.08 0.16 0.2..

Percent Change from Opt1- 50.

mum.

Pressure Maintained in Low 7.9.

Pressure Chamber, p.s.1. g.

Pressure Maintained in Bligh 10.1.

Pressure Chamber, p.s.1.g.

Pressure Difierence Between 2.2.

High and Low Pressure Chambers, p.s.i.g. Times Real Fluctuation 11 9.59.2.

It can readily be seen that the pressure fluctuation is more sensitiveto slight changes in the operation than is the pressure itself, and thatthe fluctuating pressure, after passing through a pressure booster, wasconverted into separate high and low pressures which were proportionalto the fluctuation itself with a boosting rate of 10 fold. The separatehigh and low pressures have successfully been used in conjunction with adifferential pressure transmitter and other known apparatus, such asdescribed in US. Patent No. 2,819,121, for adjusting the lift air rateto maintain optimum conditions.

The invention has been disclosed hereinabove for use and control of apneumatic lift and with respect to the figures provided with thisapplication. It is understood that the invention will have broaderutility, and alternate uses of the invention are therefore contemplated.The only limitations intended are those found in the attached claims.

We claim:

1. Apparatus for measuring the amplitude of pressure fluctuation in achamber which comprises a first detecting vessel, a second detectingvessel, a conduit connected between the first and second vessel, conduitmeans connecting at least one of the detecting vessels with saidchamber, means located in the conduit between said first and seconddetecting vessels adapted to maintain a substantially constant pressurein at least one of the detecting vessels, bleed means associated witheach constant pressure vessel adapted to prevent pressure lock whilesubstantially preventing pressure change in said constant pressurevessel for a period longer than that required for a complete wave lengthof the fluctuating pressures and a differential pressure indicatingmeans attached to both the first and second detecting vessels, adaptedto indicate the pressure difi'erential between the first detectingvessel and the second detecting vessel.

2. Apparatus for measuring the amplitude of pressure fluctuation in achamber which comprises in combination: a first detecting vessel, asecond detecting vessel, communicating conduit means between said firstand second detecting vessels, a first unidirectional fiow control meansin said communicating conduit means, adapted to allow fluid to enter thefirst detecting vessel while substantially preventing the backward flowof fluid from said first detecting vessel, a second unidirectional flowcontrol means in said communicating conduit means adapted to allow fluidto leave the second detecting vessel while substantially preventing thebackward flow of fluid into said second detecting vessel, conduit meanscommunicating the chamber with the communicating conduit means at alocation intermediate the first and second unidirectional flow controlmeans, a differential pressure transmitter attached to the first andsecond detecting vessels, adapted to determine the pressure differencebetween the first and second detecting vessels, and a recorder attachedto said differential pressure transmitter, adapted to record thepressure differential between the first and second detect- 3 ing vesselswhereby the amplitude of the pressure fluctuation in the chamber isobtained.

3. Apparatus for measuring the amplitude of pressure fluctuation in achamber which comprises in combination: a first detecting vessel, asecond detecting vessel, conduit means connected between the first andsecond vessel, a directional flow control means located in said conduitmeans, adapted to permit flow of fluid from the first to the seconddetecting vessel while substantially preventing flow of fluid from thesecond to the first vessel, a flow restricting device in said conduitmeans, located between the first detecting vessel and the directionalflow control means, adapted to substantially inhibit sudden pressurechanges in the flow control means, a connecting conduit between thechamber and the first detecting vessel, and a diiferential pressureindicating means attached to both the first and second detectingvessels, adapted to indicate the pressure differential between the firstdetecting vessel and the second detecting vessel.

4. Apparatus for measuring the amplitude of pressure fluctuation in achamber which comprises in combination: a first detecting vessel, asecond detecting vessel, conduit means connected between the first andsecond vessel, flow restricting means located in said conduit means, aconduit connecting the first detecting vessel with the chamber, and adifferential pressure indicating means attached to the first and seconddetecting vessels, so as to determine the pressure diflerential betweensaid vessels, the flow restricting means being adjusted to maintain thepressure in the second detecting vessel substantially constantintermediate the maximum and minimum pressure present in the chamber,for a period of time greater than the time required for a complete wavelength of the fluctuating pressure.

5. Apparatus for measuring the amplitude of pressure fluctuation in aliquid under pressure in a chamber which comprises in combination: afirst detecting vessel, a second detecting vessel, conduit meansconnected between the first and second vessel, a first unidirectionalvalve located in said conduit means adjacent said first detectingvessel, adapted to prevent escape of liquid from said first detectingvessel, a second unidirectional valve located in said conduit meansadjacent said second detecting vessel, adapted to prevent liquid fromentering said second detecting vessel, a connecting conduit between saidchamber and said conduit means, attached to said conduit means betweenthe first and second unidirectional valve, bleed means associated Withsaid first and second vessel, adapted to prevent pressure lock in saidvessels, a first diaphragm located across the interior of the firstdetecting vessel, adapted to provide a liquidfree gas indicating region,a second diaphragm located across the interior of the second detectingvessel, adapted to provide a liquid-free gas indicating region, conduitmeans communicating the liquid-free gas indicating re gions of the firstand second detecting vessels with a pressure differential measuringdevice, whereby the amplitude of the pressure fluctuation of the liquidin the chamber is thereby determined.

6. In a process in which a fluid pressure is developed in a confinedzone and the pressure fluctuates periodically from a maximum to aminimum value, the improved method of measuring the amplitude of thepressure fluctuation comprising transferring fluid between the confinedzone and a first indicator Zone, transferring fluid from the firstindicator zone to a second indicator zone when the pressure in the firstindicator zone rises to a predetermined value greater than the pressurein the second indicator zone, at a flow rate suflicient to maintain inthe second indicator zone a pressure intermediate the maximum andminimum pressure developed in the confined zone, restricting the flow offluid from the first indicator zone to the second indicator zone to avalue low enough to substantially suppress pressure fluctuation in thesecond indicator zone, bleeding fluid continuously from the secondindicator zone to the first indicator zone at a low enough flow rate toprevent any substantial reduction of pressure in the second indicatorzone, so as to compensate for irregular or unusual pressurefluctuations, and measuring the pressure differential between the firstindicator zone and the second indicator zone, Whereby the amplitude ofpressure fluctuation is obtained directly on a zero-shifted measurement.

7. In a process in which a fluid pressure is developed in a confinedzone and the pressure fluctuates periodically from a maximum to aminimum value, the improved method of measuring the amplitude of thepressure fluctuation comprising transferring fluid from the confinedzone to a first indicator zone When the pressure in the confined zonerises and preventing the return of said fluid from said first indicatorzone when the pressure in the confined zone falls, transferring fluidfrom a second indicator zone to the confined zone when the pressure inthe confined zone falls and preventing the return of fluid to saidsecond indicator zone when the pressure in the confined zone rises,transferring continuously a small bleed stream of fluid from the firstindicator zone to the second indicator zone, so as to correct forunusual pressure fluctuations in the confined zone, and determining thedilferential in pressure between the first and second indicator zones toobtain a continuous indication of the magnitude of pressure fluctuationin the confined zone.

References Cited in the file of this patent UNITED STATES PATENTS2,005,773 De Florez June 25, 1935 2,378,227 Lee June 12, 1945 2,445,335Philorick et a1. July 20, 1948

